Apparatus for determining optical properties of liquid samples

ABSTRACT

An apparatus for measuring optical characteristics of liquid samples, clinical samples for example, has an optical head ( 21 ) which is adapted to scan past a rack ( 12 ) of sample containers first in one direction and then in the opposite. The optical head has reference and test light sources ( 22 ) and corresponding light detectors ( 28 ) and separate optical paths are provided in the head for developing reference and test beams passing through the scanned samples. A fixed band pass filter is provided in the reference path and a filter wheel with a plurality of different band pass filters is provided in the test path, the apparatus being arranged to index the requisite filter into the test path in dependence upon the results of the reference scan. The optical head is driven by a reversible stepper motor ( 26 ) via a toothed drive belt ( 27 ) and this enables the output signals from the detectors to be correlated to the specific samples in the rack.

FIELD OF THE INVENTION

The present invention relates to an apparatus for determining opticalproperties of liquid samples. More particularly, but not exclusively,the invention relates to an apparatus for carrying out tests pertainingto chemical chemistry, enzyme immuno assays (EIA), enzyme linkedimmunosorbent assays (ELISA) and turbidimetric assays for example.

BACKGROUND OF THE INVENTION

Various optical arrangements are known for measuring and analysingbiological/chemical test samples. For example, conventionalspectrophotometers are available commercially, but such instruments aretypically bulky, not inexpensive and require a high degree of operatorskill or specialisation. Various automated analysis systems of the kinddescribed in U.S. Pat. No. 3,770,382 and U.S. Pat. No. 3,897,216 arealso known, in which the sample cells are transported sequentiallythrough a test station on a conveyor chain during the course of a testoperation. Such systems are typically large and complex in design andare correspondingly expensive. Further, optical density measuringapparatuses of the kind described in U.S. Pat. No. 4,729,661 are knownin which the specimens are contained within a cuvette tray and movementof the cuvette tray through a test station is effected by translatingthe tray along an open channel defined in and along the front edge ofthe chassis of the apparatus.

In the above-mentioned prior art devices, sample cells are passedsequentially through a beam of light and the light signal transmittedtherethrough is then detected and processed. Typically the sample cellsare in the form of expensive microcuvettes having optical quality facesto ensure that test results are not degraded by imperfections in thesample containers. The prior art devices also commonly have had toemploy a number of light sources to ensure that a sufficiently highlevel of light intensity is produced over a broad spectral band ofwavelengths. For example, special-design light bulbs have had to beemployed to perform measurements in the ultraviolet waveband. In theknown devices, it is also difficult to position or locate accurately thesample(s) with respect to the light beam which adds an unwanteduncertainty to each measurement.

The aim of the present invention is to provide an improved apparatuswhich overcomes or substantially reduces at least some of theabove-discussed drawbacks and limitations.

SUMMARY OF THE INVENTION

According to the present invention there is provided an apparatus fordetermining optical properties of liquid samples held in transparentcontainers, said apparatus comprising:

means defining a mounting for a plurality of said containers in a lineararray;

an optical head mounted for translation along the length of said array,said optical head including a light source on one side of the array, alight detector on the other side of the array for detecting light fromthe source after it has passed through the array, and means defining anoptical path between the source and the detector such that in use of theapparatus the light from the source scans across the liquid samples asthe head is moved; and

means responsive to the output of said light detector during translationof the head along the length of the array for determining the opticalproperties of each of the samples in the array.

A housing of the apparatus is advantageously provided with an opening atits upper surface for receiving a carrier which defines the mounting forthe containers in the linear array. The array may be in the form of arectilinear array, and the optical head may be arranged so as to moverectilinearly.

The housing of the apparatus and the carrier may be configured so as toinhibit the passage of extraneous light through the housing opening whenthe carrier is inserted.

Further, the optical head may be mounted on a carriage, oralternatively, the optical head may comprise a carriage. The carriageis, advantageously, engaged with one or more guide rails in theapparatus to permit movement of the optical head/carriage along thelength of the rails. The carriage may also comprise linear bearing meanswhich ensures easy movement of the optical head/carriage along therail(s). Advantageously, the carriage includes spaced-apart wheelsadapted to run on a support track provided in the apparatus. The wheelsmay be configured so as to produce a (sufficient) reaction force whichbiases the carriage into firm contact with the rail(s).

Furthermore, the apparatus may include an electric drive motor coupledto the carriage by means of a drive belt. The electric drive motor ispreferably in the form of a reversible stepper motor. The drive belt ispreferably in the form of a toothed belt. Such an arrangement enables acontrolled movement of the optical head past the array of samples andalso enables a corresponding controlled analysis of the output of thelight detector for each sample.

The apparatus may provide means for supplying pulsatory drive signals tothe drive motor and means for correlating the output of the detectorwith the positions of the samples in the array.

The apparatus may provide processor means for controlling theapplication of drive signals to the motor and for effecting sampling ofthe detector output, thereby identifying in the detector output thatsignal portion which corresponds to each of the samples. The processingmeans may also be arranged to effect a curve fitting algorithm upon thesignal portions associated with the separate samples. Such a curvefitting algorithm may be structured to take no account of glitches inthe signal portions corresponding to imperfections in the containers. Inaddition, the processing means may be arranged to derive a weightedaverage of the signal portions associated with the samples. This kind ofprocessing advantageously enables high precision, reproduciblemeasurements to be made on test samples contained in simple test tubesas opposed to in expensive microcuvettes.

The optical head may preferably comprise a solid block (for example,made of aluminium alloy) defining a mounting for the light source, amounting for the light detector and a recess for the passage ofcontainers through the optical head when the head is moved duringoperation of the apparatus. The provision of such a block head limitsunwanted aberrations in the optical path and inhibits the passage ofextraneous light through the apparatus. Further, the provision of amoving head past the samples permits the apparatus to be in a compact,portable form. The apparatus may, for example, fit into a briefcase.

Advantageously, the optical head may include a filter carrier (forexample, a filter wheel system) having a plurality of different bandpassor interference filters mounted therein. The apparatus may also beadapted and arranged to introduce automatically the requisite filterinto the optical path.

Preferably, the apparatus may include a bar code reader for enteringinformation into the apparatus so as to condition the apparatus for theperformance of specific optical property tests.

The apparatus may further include means for adjusting the power suppliedto the or each said light source so as to determine the optimum spectraloutput and/or the intensity thereof. Standard tungsten-halogen bulbswith a quartz envelope may, for example, be employed to performmeasurements in the ultraviolet waveband.

The apparatus may be used to carry out numerous routine and specialitylaboratory tests quickly and to a high precision. Use of the apparatusdoes not require a high degree of operator skill or specialisation. Theapparatus may be mains-operated or operated from batteries.

The above and further features of the present invention are set forth inthe appended claims and, together with advantages thereof, will becomemore clear from consideration of the following detailed description ofexemplary embodiments of the invention given with reference to theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a schematic plan view of an exemplary apparatus embodyingthe present invention;

FIG. 2 shows a schematic and elevation view of the apparatus of FIG. 1;

FIG. 3 shows a perspective view of the external appearance of anotherapparatus embodying the invention;

FIG. 4 shows a schematic block diagram view of the apparatus of FIG. 3;and

FIGS. 5 to 7 are views showing in more detail the component parts of theapparatus of FIGS. 3 and 4, FIG. 5 showing the apparatus in top planview, and FIGS. 6 and 7 showing the same apparatus in front elevationand side elevation views.

FIGS. 8(a) to 8(b) show the structure of the optical block headcomponent in more detail.

DETAILED DESCRIPTION OF THE EMBODIMENTS INVENTION

The embodiment of FIGS. 1 and 2 is only schematically illustrated andwill be discussed in general terms hereinafter before a particular anddetailed description is provided of the embodiment of FIGS. 3 to 7. Inthe embodiment of FIGS. 1 and 2, the samples are preferably held intransparent containers arranged in a linear array. The light emitter andlight detector are mounted on a track with the light emitter on one sideof the array and the light detector on the other side of the array withthe emitter and detector aligned appropriately. The emitter and detectorcan move past the transparent containers in both directions. The emitterand detector are mounted with a gap between them into which transparentcontainers can be placed, for example the transparent containers can bemounted in a pre-loaded cassette which fits in the equipment, so thattransparent containers can be easily replaced.

In order for different wavelengths of light to be used, there is a meansto enable a filter to be positioned in the light beams from the emittereither before or after it passes through the transparent containers.There are means to change the filter so that different filters can beused for different transparent containers. The filters are bandpass orinterference filters which pass a selected spectrum or wavelengths oflight.

There are two light emitters and corresponding detectors positioned topass light through the transparent containers with one light sourcebeing used as a reference and the other light being used to detect thedifference in absorption or reflectance at a second wavelength orspectrum of wavelengths.

In order to avoid errors due to the difference in intensity of the lightfrom two independent light sources, a transparent container containingliquid of known absorption can be used to obtain a measurement from bothlight sources and the microprocessor and regulator can thenautomatically make any adjustment required to obviate any difference inthe intensity of the light from the different light sources.

This ability is also used to help increase the life of the lamps used asthe light source, by causing the power into the lamp to be changed asthe output grows dimmer, therefor bringing the light output back to therequired level.

In word, the wavelength of the light can be chosen by choice ofdifferent filters, so that a particular reagent or compound can bedetected, making it possible, with the same liquid in each transparentcontainer, to detect more than one reagent or compound. The output fromthe detector can be fed into a computer for processing, e.g so that aprinted output can be obtained. The same compound can be used to controlthe operation of the emitter and detector and other components.

Preferably, there is a light emitter which emits light which passesthrough two side by side filters, the first of which transmits light ofa frequency which is substantially not affected (e.g. absorbed orreflected) by the reagents or compounds in the liquid in the transparentcontainers which are to be detected, measured or analysed and the secondfilter transmits light of a frequency which is so affected.

The light from the first filter passes through the liquid in thetransparent containers or, preferably, passes through the filter afterit has passed through the transparent container, and acts as standard orreference to measure the degree of absorption or reflectance of theliquid. The light from the second filter measure or detects the changein the reagents or compounds in the liquid. This arrangementsubstantially reduces zero errors etc. and gives a measure of thedifference of absorption or reflectance at the two spectrum bandwidthscorresponding to the light passing through the filters.

There can be a means to change the second filter in a preselected mannerso that a particular filter can be used at a particularly transparentcontainer, this can be done for example by a switch moving a carousel onwhich are mounted a series of different filters; the switch can operateat one end of the movement of light emitters and detectors along thetrack.

Preferably when the light source and its corresponding detector passesdown the track in one direction the reference light source isoperational and when it passes back down in the opposite direction backto the start position the other light source is operational.

In order to measure a property such as the optical density of a liquidin a transparent container, a series of readings can be taken as thelight source passes across each transparent container, with the lightintensity measured by the detector. By the use of a microprocessor theaverage optical density for each sample in each transparent containercan be obtained. Preferably, the movements of the emitter and detectorare operated by a stepper motor so that the speed past each transparentcontainer can be controlled.

By use of microprocessor control and filter changes, it is possible tohave a preselected filter used for any particular transparent container;preferably, the operation of the equipment is controlled by amicroprocessor so that the equipment will run automatically and theresults obtained as readings or a print out etc. in the desired form.

When two independent light sources are used one source can be anultraviolet emitter which will then also enable the system to operate asa fluorescence detector.

Referring now to FIGS. 1 and 2, there are shown therein in schematicplan and end elevation views the essential component parts of anapparatus embodying the invention. The apparatus generally indicated at(10) includes a track (1) having light emitters (2) and light detectors(3) mounted on it so they can be moved as shown in FIG. 1. Transparentcontainers (4) can be placed in a cassette (7) which fits in the gap(6). During a scan, light emitted from the light emitters (2) passesthrough each of the transparent containers (4), through filters (8) and(9) mounted in filter holding means (5) into the light detectors (3).The filter (9) can be changed so that different wavelengths of light canbe used.

The filter (8) passes light of a wavelength substantially unaffected bythe reagents or compounds which are to be detected, so that it providesa reference signal, and the filter (9) is chosen in accordance with thereagent or compound to be detected and the difference in the signals isa measure of this reagent or compound.

In use, the transparent containers (4) containing the liquid whoseoptical properties are to be determined are placed in cassette (7) inposition in the equipment. One of the light emitters (2) is turned onand acts as a reference and the light passes through filter (8), asshown. The emitters (2) and detectors (3) are connected to a movabletrack (1) together and automatically aligned. The emitters (2), filterholder (5) and detectors (3) move sequentially past the transparentcontainers (4) down the track in one direction and the light passingthrough them is detected by the detectors to enable optical propertiesat the spectrum of filter (8) to be determined. When the end of thetrack is reached the other light source is then turned on and the lightpasses through container (4) and filter (9) and the emitter and detectorthen pass down the track (1) in the opposite direction and the opticalproperties are determined from the spectrum of filter (9).

There are a series of filters (9) in the filter holder (5) to enabledifferent spectra of wavelengths to be used for the transparentcontainers. When the emitter reaches the end of the track, and before itis reversed, the filter (9) can be preselected.

The movement of the light emitters (2) and light detection (3) along thetrack, and the operation of the apparatus is controlled by amicroprocessor which can automatically process the signals, compare theresults at the different spectra of wavelengths and print out theresults in the desired form.

Referring next to FIG. 3, there is shown therein a perspective view ofthe external appearance of an actual apparatus (10) embodying theinvention. As shown in the figure, the apparatus may be provided with acassette or rack (12) into which up to twelve test tubes or microwells(11) may be loaded. Cassette (12) is suitably dimensioned for insertioninto the apparatus (10). All information concerning the optical propertytests and the corresponding mathematical reductions required to carryout such tests may be input by optical barcode (18) by use of a lightpen (17). Each of the test tubes or wells may be read up to 3,000 timesthereby rendering exceptional reproducibility during the course ofmeasurement and the results can then be averaged and printed out on aprinter. In addition, the results can be downloaded onto a personalcomputer by virtue of the provision of an RS232 port in the apparatus.The apparatus (10) as shown is portable and fits into a briefcase. Itsdimensions are typically 365×310×50 mms and has a weight of less than 2kgs. As part of the user interface, there are two main buttons (15,16)corresponding to “no” and “yes” and two other buttons (13,14)corresponding to “scroll up” and “scroll down”. The apparatus also has aslot (20) for feeding printer paper therethrough.

A person wishing to perform a test scan by use of the apparatus (10)must carry out a series of operations in a specific order namely:

first switching the apparatus on which causes a visual display (19) toask for information so as to condition the apparatus for the performanceof the test,

then scribing in information using the barcode reader and pen (17,18) orwith a keyboard coupled to the RS232 port,

inserting the cassette (12) of test tubes (11) into the apparatus andpressing the “yes” button (16).

In the event that the wrong information is scribed in, the button “no”may be pressed.

Given that the “yes” button is pressed, the optical head of theapparatus (not shown in FIG. 3) proceeds to scan across each of thesamples held in the cassette.

A discussion of the controlled scanning movement of the optical headpast the array of samples will follow.

FIG. 4 shows a schematic view of the assembly of component parts of theapparatus embodying the invention. The apparatus comprises an opticalhead (21), preferably in the form of a solid block made of aluminiumalloy, which is mounted for translation along the length of theplurality of containers (11) arranged in linear array, the optical headfurther defining a mounting (22) for the light sources, a mounting (28)for the light detectors, and a recess (23) for the passage of containers(11) through the optical head (21) when the head is moved duringoperation of the apparatus. It is to be noted that light emitted by thelight source is channelled through the block head (21) thereby definingthe optical path and intercepting the recess (23). As shown in thisfigure the solid block (21) comprises mountings for separate test andreference light detectors (28) and separate channels are providedthrough said block to define said separate test and reference channels.

FIG. 4 shows the interaction between the optical head component part andthe stepper motor and the processor/software unit. As shown, theapparatus comprises a reversible stepper motor (26) coupled to theoptical head (21) by means of a drive belt (27). The drive belt (27) isenvisaged to be a toothed belt and the arrangement is such that itenables a controlled movement of the optical head (21) past the array ofsamples in the containers (11) and a corresponding controlled analysisof the output of the light detector for each sample. As shown, theapparatus may also comprise means for supplying pulsatory drive signalsto the stepper motor and for correlating the output of the detector withthe positions of the samples in the array. It is to be noted that theprocessing unit which is preferably in the form of microprocessor (25)may be used to control the application of drive signals to the motor andcorrespondingly to effect sampling of the detector output so as toidentify in the detector output that signal portion which corresponds toeach of the samples. The processing unit (25) is arranged to effect acurve fitting algorithm upon signal portions associated with theseparate samples. Furthermore the curved fitting algorithm is structuredto take no account of glitches in signal portions corresponding toimperfections in the containers (11). The microprocessor may be arrangedfurther to derive a weighted average of the signal portions associatedwith respective samples, the weighting being effected in considerationof the cross-section or shapes of the containers.

During the course of a scanning measurement, the microprocessor basedcontrolled system (25) is adapted and arranged such that the opticalproperties of the samples are determined by first effecting a referencescan of the samples by translation of the optical head (21) along thelength of the linear array and then effecting a test scan in theopposite direction by way of a further translation of the head along thelength of the array. In this regard, according to the informationscribed in by the barcode pen (17), selection of a reference filter andof an appropriate optical filter for the test scan may be automaticallyeffected by the apparatus. In FIG. 4, the appropriate filters (referenceand test) are introduced into the optical path at positions 24,24′ asdefined in the optical head (21). The optical head (21) includes afilter carrier in the form of an indexable filter wheel having a varietyof different bandpass or interference filters mounted therein and whichwheel is arranged to co-operate with abutment means (29) at one end ofthe range of movement of the optical head (21) for indexing the wheel byone position. Such an arrangement enables the filter wheel to be indexedto any desired position by controlled reciprocation of the optical headat said one end of its range of scan movement.

It is to noted that the processor/software unit (25) samples andconverts the output analogue signal of the light detectors into adigital form and, inter alia, smooths and averages and combines thedigital data in a weighted fashion so as to enable optical properties ofthe samples to be determined. Typically, the smoothed/averaged referencescan data are subtracted away from the smoothed/averaged test scan datato eliminate unwanted intrinsic effects of the instrumental response(such as noise). Furthermore, the unit (25) includes means for adjustingthe power supplied to each said light source to determine the spectraloutput and/or the intensity thereof. The apparatus further includes aprinter (31) and/or visual display (30) together with an RS232 port viawhich results can be downloaded onto a personal computer.

Finally, FIGS. 5 to 7 show in more detail the same component parts ofthe apparatus embodying the invention in top plan, front elevation andside elevation views. The Figures again use the same reference numeralsas were used to designate same/like parts in the description of theprevious Figures.

FIG. 5 shows the construction of the optical head (21), in furtherdetail, and its interaction with other parts of the apparatus embodyingthe invention in top plan view. The head (21) in the form of a solidblock is shown to have mountings for separate test and reference lightsources (22), mountings (28) for separates test and reference lightdetectors and separate channels (35,36) provided through said block (21)so as to define separate test and reference channels (35,36). In such anarrangement, the reference scan is effected by use of the referencechannel (36).

The block head (21) includes a recess portion (23) for the passage ofcontainers which hold samples therein as the head is moved along thelength of a guide rail (40) of the apparatus. The block head (21) alsodefines a mounting for the reference and test filters (24,24′).Preferably, and indexable filter wheel for carrying a plurality ofdifferent bandpass or interference filters mounted therein can bemounted at position 24′ in the block and a suitable reference filter canbe mounted at position 24 in the block. The filter wheel may be arrangedto co-operate with abutment means, for example, with a top and bottomratchet spring (29,29′), at one end of the scanning head's range ofmovement, the arrangement being such that the filter wheel can beindexed to any desired position automatically by controlledreciprocation of the head at said one end of its range of movement.

The head's range of movement is defined by use of the stepper motor(26), a toothed belt (27) which is engaged with the head and by opticallimiting switches (38,38′) which serve to define the start and endpositions of the scan across the linear array of samples. It is to benoted that the drive belt (27) is engaged with a slot (37) the opticalhead.

As shown, the back of the apparatus includes the electronics andsoftware (25) and an air vent (39).

As regards selection of the spectral range of the light sources mountedat positions (22) in this arrangement, bandpass or interference filtersare preferably used which typically have a bandwidth of 10 nanometersand which cover a waveband between 300 nanometers to 700 nanometers.

FIG. 6 shows the apparatus of FIG. 5 in front elevation view. Theapparatus includes an external housing (48) enclosing the optical headarrangement (21), a guide rail (40) along which the head is adapted tomove, and the stepper motor system (26). The separate parts of the motor(26) including the motor gearbox (49) and the motor drive spindle (50)are shown in the Figure. The optical head (21) is adapted to run on asupport track (45) provided in the apparatus, the track being supportedin the housing (48) by means of mounting pillars (47). The bottom end ofthe support track (45) in the apparatus is designed to coact with theoptical limiting switches (not shown here). Further, the optical head(21) is shown to be mounted on a carriage portion (46) which is engagedwith the guide rail (40) in the apparatus so as to be movable along thelength of the rail.

FIG. 7 shows the same apparatus of FIGS. 5 and 6 in side elevation view.The carriage portion (46) is shown here in more detail and includeslinear bearing means which ensures easy movement of the carriage alongthe guide rail (40). The carriage (46) includes spaced apart oversizedwheels (44,44′) which are adapted to run on the support back (45)provided in the apparatus. The oversized wheels (44,44′) are configuredto provide a reaction force such as to bias the carriage into firmcontact with the guide rail (40) of the apparatus. The optical head (21)is also shown to include a lens arrangement in which a pair of lenses(42,43) are provided in the channels of the block head for establishingsubstantially parallel light beams across the recess portion (23). Acover portion (41) is engageable with the upper surface of the opticalhead so as to cover the recess portion (23) and block extraneous lightfrom entering through the housing opening. The light source mounted atposition 22 of the head is preferably a tungsten halogen lamp with aquartz envelope. For sake of completeness FIG. 7 shows mounting means(50) for the electronics of the instrumentation. The bottom end of thesupport track (45) is also shown to coact with the slotted opticallimiting switches (38) of the apparatus.

Finally, FIGS. 8(a) and 8(b) show the structure of the above-describedoptical block head (21), in more detail, in plan and side views. Typicalblock dimensions in millimeters are as shown. The block is preferablyformed of aluminium alloy material. The figures again use the samereference numerals as were used to designate same/like parts in thedescription of FIGS. 4 to 7.

It should be noted from FIGS. 8(a) and 8(b) that the block head (21) hasmountings for separate light sources (22), mounting for separate lightdetectors (28), a recess portion (23), and separate channels (35,36)running therethrough so as to define separate test and referencechannels. During operation of the apparatus, the reference scan filteris inserted into position (24) of the block (21), and the filter wheelcarrier which has a selection of optical filters mounted therein isinserted into position (24′) of the block (21). The drilled holes(60,61) formed in the upper block surface are adapted to receive screwsfor attachment of a cover to the said upper block surface.

In operation of the machine of FIGS. 3 to 8 hereinabove described, theuser switches on the machine and a display appears on the machine askingfor information. The user can then scribe in information relevant to thetest which is to be conducted by means of the bar code reader or by useof a keyboard connected to the RS232 port. A rack of test samples isthen loaded into the slot in the top of the machine housing and themachine display then indicates an option to select “go” to initiate thetest. The optical head of the machine then traverses the rack of samplesfrom one side to the other and takes a reference reading of each tube,the reference light source being illuminated and the output of thereference detector being active. Having traversed the array of samples,the machine then selects the appropriate filter to be employed duringthe subsequent test scanning of the samples, this selection beingeffected in dependence upon the data entered into the machine by use ofthe bar code reader or other input device and in dependence upon theoutput of the reference detector during the reference scan of theoptical head past the sample array. The selected filter is indexed intothe optical path between the test lamp and the test detector byreciprocation of the optical head at the end of its reference travel. Anoptoelectronic detector ensures that the operating system “knows” thehome position of the filter wheel and thus “knows” the whereabouts ofeach filter in the wheel.

Having selected the appropriate filter and introduced it into the lightpaths between the test light source and the test detector, the steppermotor is reversed so as to cause the optical head to scan back acrossthe array of samples and the corresponding output of the test detectoris processed.

The analogue outputs of the reference and test detectors are convertedinto digital signals with correlation with the stepper motor and drivebelt position so that the machine “knows” which sections of the signalscorrespond to which samples. The digital signals are processed using acurve-fitting algorithm designed to discard aberrant signals (glitches)arising for example on account of scratches or other imperfections inthe sample containers. A centre point is identified in the resultantcurve for each sample and a weighted average is derived for each of thereference and test curves by sampling the curve at predeterminedlocations on each side of the centre point, the weighting being effectedinter alia in dependence upon the cross-sectional shapes of the samplecontainers. Having derived weighted reference and test averages for eachsample, these two averages are processed to obtain an indication of theoptical characteristics of the samples, particularly their opticaldensities, and a corresponding record is provided on the printer or, viathe RS232 port, to a computer monitor.

Having thus described the present invention by reference to exemplaryembodiments, it is to be appreciated that modifications and variationsthereto are possible without departure from the spirit and scope of thepresent invention. For example, a single channel or a plurality ofchannels may be provided through the optical block head so as to definethe test and reference channels during the scanning process. Inaddition, whereas in the described exemplary embodiments the opticalhead is mounted on a separate carriage portion, the opticalhead/carriage can alternatively be of a kind comprising aintegrally-formed unit.

What is claimed is:
 1. An apparatus for determining optical propertiesof liquid samples held in transparent containers, said apparatuscomprising: a housing having an opening in an upper surface thereof forreceiving a carrier which is adapted to receive a plurality of saidcontainers in a rectilinear array, the arrangement being such that whenthe carrier is loaded with containers and is inserted into said openingliquid samples in the containers locate in predetermined positionswithin the housing; an optical head mounted within said housing forrectilinear reciprocal translation along the length of said array, saidoptical head comprising a solid block having a recess therein whichlocates with said array and having a first portion on one side of thearray and a second portion on the opposite side of the array; at leastone light source mounted on said first portion of said solid block andseparate test and reference light detectors mounted on said secondportion; first and second light channels formed in said block betweensaid at least one light source and said test and reference detectors,said channels intersecting said recess and being arranged such that inuse of the apparatus a substantially parallel beam of light from said atleast one source scans across the light samples as the optical head ismoved and is received by said detectors after passage through thecontainers and the samples therein; filter means comprising a pluralityof individually selectable optical filters provided in the optical pathto at least said test light detector; an electric drive motor coupled tosaid optical head for effecting reciprocal movement thereof; and controlmeans including data input means accessible to a user of the apparatusfor enabling the operation of the apparatus to be predetermined inaccordance with entered data, said control means being arranged todetermine the operation of said motor and said filter means and toeffect sampling of the light detector outputs to identify thereinrespective signal portions corresponding to each of the samples, saidcontrol means being arranged to determine the optical properties of theliquid samples by first effecting at least one reference scan bytranslation of said optical head along the length of the array and theneffecting at least one test scan by further translation of the opticalhead along the length of the array.
 2. An apparatus as claimed in claim1 wherein housing of the apparatus and the carrier are so constructedand arranged as to inhibit the passage of light through the housingopening when the carrier is inserted.
 3. An apparatus as claimed inclaim 1 wherein the control means includes a microprocessor arranged toeffect a curve fitting algorithm upon the signal portions associatedwith the separate samples.
 4. An apparatus as claimed in claim 3 whereinthe curve fitting algorithm is structured to take no account of glitchesin the signal portions corresponding to imperfections in the containers.5. An apparatus as claimed in claim 3 wherein the microprocessor isarranged to derive a weighted average of the signal portions associatedwith respective samples, the weighting being effected in considerationof the cross-sectional shapes of said containers.
 6. An apparatus asclaimed in claim 1 wherein said optical head includes a carrier having aplurality of different filters mounted therein, and the apparatus isadapted and arranged automatically to introduce the requisite opticalfilter into the optical path.
 7. An apparatus as claimed in claim 6wherein the carrier is an indexable filter wheel and means are providedin the apparatus for indexing the wheel to a relevant position.
 8. Anapparatus as claimed in claim 7 wherein said filter wheel is arranged toco-operate with abutment means at one end of the range of movement ofthe optical head for indexing the wheel by one position, the arrangementbeing such that the filter wheel can be indexed to any desired positionby controlled reciprocation of the optical head at said one end of itsrange of movement.
 9. An apparatus as claimed in claim 1 wherein lensmeans are provided in said channels for establishing substantiallyparallel light beams across said recess.
 10. An apparatus as claimed inclaim 1 wherein the solid block has separate test and reference lightsources associated with said separate channels.
 11. An apparatus asclaimed in claim 1 wherein the control means includes a microprocessorarranged to process the outputs of the reference and test detectorsseparately and then to combine the results or the reference and testprocesses in determining the optical properties of the liquid samples.12. An apparatus as claimed in claim 1 including means for adjusting thepower supplied to each said light source to determine the spectraloutput and/or intensity thereof.
 13. An apparatus as claimed in claim 1including a bar code reader for entering information into the apparatusto condition the apparatus for the performance of specific opticalproperty tests.
 14. An apparatus as claimed in claim 1 including aprinter and/or visual display.
 15. An apparatus as claimed in claim 1including a visual display.